This invention relates to a die press having selectively variable die access clearance and more particularly, to such a press having unique means incorporated therein whereby the press may be normally operated with normal minimum die access clearance, yet when required, the die access clearance may be quickly increased and then eventually quickly returned to original minimum form, all without otherwise altering the die securement when returned to its original form. The overall result is that original die adjustment is always retained when the die is in normal working position with its minimum working die access clearance, but upon the necessity arising for temporary increased die access clearance, the same can be quickly provided and upon return to normal, all original conditions will be automatically restored.
Presses of the type reciprocating dies toward and away from each other have usually included a movable ram securing and carrying a first die and a stationary press bed securing a second die. Furthermore, in modern high-speed production lines, the movable ram will reciprocate on a continuous repeating basis with material to be worked upon by the dies, such as, metal, being fed therebetween when the dies are spaced apart a maximum distance in the cycle with a predetermined die access clearance. For maximum speed of continuous press operation, the prime consideration of this predetermined die access clearance when the dies are spaced a maximum distance apart is a sufficient clearance space for the feeding of the material or part to be worked upon by the dies therebetween and into position for being worked upon by the dies, as well as removal of the finished part in some cases depending on the particular type of dies and working operation involved.
An important secondary consideration in the predetermined die access clearance is normal minor die maintenance which can be required due to normal wear and tear, and the removal of improperly formed parts from between the dies which can occur for various reasons including improper material thickness of improperly preformed parts fed between the dies for that particular metal working operation. With the press operating on a normal continuous basis, when minor maintenance cannot be performed or an improperly formed part occurs which cannot be cleared from the dies during a normal press cycling operation, the operation of the press must be immediately stopped, usually through automatic improperly formed part detection and automatic press control. The minor maintenance must then be performed and/or the improperly formed part or parts must then be removed prior to resumption of the automatic press operation.
Thus, in constructing a press of the type herein involved for operation in a high-speed production line, two basic choices for predetermined die access clearance are presented, particularly where the press is normally continuously operable with a predetermined die access clearance and when minor die maintenance is needed or improperly formed parts occur, a greater die access clearance is frequently required for the maintenance or the removal of the improperly formed parts. For maximum speed of press operation under normal production conditions with properly formed parts being produced, the predetermined die access clearance should be a minimum, just that required for automatically feeding material between the dies on a normal production basis. However, if that normal production predetermined die access clearance will not be sufficient for at least the usual minor maintenance and the usual removal of improperly formed parts from between the dies when that is required or occurs, either the predetermined die access clearance must be increased sufficient for such maintenance or improperly formed part removal which will necessarily decrease the speed of normal continuous press operation or one or both of the dies must be removed from the press for the maintenance or improperly formed part removal. In either case, the effective production output of the press will necessarily be inhibited.
An additional consideration in the construction of presses for high-speed die operation is that of die attachment to the press for maximum die accuracy. In modern production processes, it is frequently required to die form metal parts of a few thousandths of an inch thickness while maintaining a uniform accuracy of a few ten thousandths of an inch. Obviously this accuracy of formation is made more difficult with higher and higher required speed of production and, in addition to die construction accuracy, is greatly affected by the manner in which the dies are attached to the press, again the speed of operation being a factor.
It is common practice in modern press construction for such high-speed work to attach the dies by the very closely predicated use of tensioned bolts. The usual procedure is to initially attach the dies to the press with particularly located fastening bolts which are only initially slightly tensioned and then by a very closely controlled bolt tightening procedure, tensioning each of the fastening bolts in a precalculated manner for obtaining the required die alignment as well as secure retainment of the dies for maintaining such alignment during the high-speed reciprocal movement thereof. It can be understood, therefore, that the attachment and securement of the dies is a very tedious and time consuming process.
Thus, this required method of die attachment is a factor of consideration in the choices of press construction as hereinbefore discussed. If the choice of press construction is that of merely providing predetermined die access clearance under normal operation sufficient for the automatic feeding of the material to be formed between the dies, thereby requiring detachment of the dies from the press for required minor maintenance and/or for removal of improperly formed parts, this die removal and tedious re-attachment becomes a production time decreasing factor. In other words, although the use of the lesser predetermined die access clearance will greatly increase production speed, each time that minor maintenance is required or an improperly formed part occurs requiring die removal and replacement, the overall production speed benefits will be reduced.